These studies use neuroscience and ethopharmacological methods to investigate the mechanisms related to production and perception of the isolation call and related vocalizations in nonhuman primates as a model for understanding the neurology and physiology of the vocal expression of affect in human in impact of crying on the listener. Major findings this year were as follows: 1) intravenous infusion of 0.5 M sodium lactate in squirrel monkeys caused a reliable, brief period of tachycardia (similar to the cardiac reaction in human subjects to this procedure) followed by prolonged bradycardia. Addition or CCK-4 to the infusate produced a more pronounced sympathetic arousal (facial flushing) but failed to further increase the depth of tachycardia. 2) analysis of heart rate and vocal behavior in 3-5-month old, peer-reared infant rhesus macaques during 30 min. periods of social separation indicated a significant positive correlation between cardiac reactivity and vocal reactivity to this mild stressor. Fewer mother-reared infants showed a significant correlation between these measures. No significant differences according to rearing condition were found for calling rate or heart rate. However, there was a significant difference in locomotor activity, peer-reared animals having higher activity levels. Males and females differed significantly in mean rate of vocalizing and in variability of calling over 30 minutes, females having both higher rates overall and exhibiting more variability within trials. 3) Comparison of the frequency variability of the cries of human infants suggested stability in the same infants at 1 and 40 weeks of age, but significant differences in other measures according to the distress level of the infant.